Recently, in the market, there is a strong interest in films having excellent chemical resistance, thermal resistance, hardness, folding resistance, and whitening-upon-folding resistance. Specifically, they are used, for example, as films used to laminate vehicle interior or exterior parts as a coating substitute, films used as a floor material, and the like. However, conventional acrylic films do not have sufficient chemical resistance, thermal resistance, hardness, folding resistance, and whitening-upon-folding resistance, which are properties needed for these applications.
Polyglutarimide obtained by treating an acrylic-based resin with an imidizing agent, thereby introducing an imide group into a high-molecular weight chain, is known as a resin that can be provided with chemical resistance, thermal resistance, and hardness. In particular, an imidized acrylic resin, that is obtained by copolymerizing methacrylic acid and/or tertiary-butyl methacrylate with methyl methacrylate using a solution polymerization method or block polymerization method, heating the resultant to form an acid anhydride unit, and then reacting this unit with an imidizing agent, is disclosed as a resin having excellent thermal resistance and chemical resistance (see Patent Document 1).
However, this resin is very brittle, and, thus, there is a problem in which, when the resin is formed into a film and used to laminate a base material, the folding resistance of the film, which is needed as a property for such treatment, is poor.
Thus, in order to address this problem, an imidized acrylic resin having excellent chemical resistance, thermal resistance, and hardness, and improved folding resistance and whitening-upon-folding resistance, obtained by treating a methacrylic-based resin composition with an imidizing agent is disclosed in which the methacrylic-based resin composition comprises a methacrylic acid ester-based polymer and an acrylic acid ester-based crosslinked elastic particle each having specific constituent materials. The average particle size of and the amount of polyfunctional monomer used in the crosslinked elastic particle (B) satisfy a specific formula (see Patent Document 2). This fluidized acrylic resin has excellent chemical resistance. However, a chemical resistance that is also effective against a sun-screening agent (e.g., Coppertone (registered trademark)) and the like has come to be required in recent applications to vehicle parts, and, thus, there is a demand for further improvement in the chemical resistance to such specific agents.
Also, a rubber-containing acrylic resin having improved thermal resistance, solvent resistance, and optical isotropy, comprising glutaric acid anhydride groups formed by heating a resin copolymerized in advance with 15 to 50 wt % of unsaturated carboxylic acid, is disclosed (see Patent Document 3). In the case where a large amount of acid anhydride groups are contained as in this resin, resistance to an organic solvent and the like is excellent, but there is a problem in that the resistance to an aqueous alkali solution and the like becomes poor.
Thus, there is no resin in which the resistances to various agents are well balanced and there is a demand for the development of such a resin.
Conversely, an imidized acrylic resin and a glutaric acid anhydride-containing resin have high melt viscosities, and, thus, there is room for improvement in that film defects such as die lines occur when the resins are molded into a film using a T-die-equipped extruder or the like, and productivity is lowered when foreign substances are melt-filtered.    Patent Document 1: JP S62-4704A    Patent Document 2: JP 2005-290136A    Patent Document 3: JP 2004-292812A